On the Aux track, cut everything below 3kHz–5kHz with a steep slope.
The original Aphex unit worked by high-pass filtering the signal, adding slight harmonic distortion (saturation), and mixing it back with the original signal. You can recreate this "secret" trick for free in any DAW: aphex vintage aural exciter crack
It uses similar dynamic excitation technology to add "brilliance" and "shine" to vocals and mix busses. How to Achieve the "Exciter" Effect Manually On the Aux track, cut everything below 3kHz–5kHz